Table 1.

Physicochemical characteristics of the environmentally resistant stages of Giardia duodenalis, Cryptosporidium spp., and Toxoplasma gondii

Characteristic	Giardia duodenalis cyst	Cryptosporidium oocyst	Toxoplasma gondii oocyst	References
Size (μm)	7–10 × 5	3.8–6.3 × 4.6–8.4a	10 × 12	11, 60, 109
Wall
Thickness (nm)	300–500	50–80	∼100	14, 37, 57
Number of layers	2	3	2
Outer wall thickness (nm)	250	8	30
Surface biochemistry	Matrix of filamentous GalNAc homopolymer and Cys-rich proteins	Glucose-rich glycocalyx	Possible polymeric cross-links of Cys- and/or Tyr-rich proteins	14, 37, 57, 64, 76, 103
Zeta potential (mV)	−33.5 in distilled H2O at pH 6.4	−25.0 in deionized H2O (conductivity, 83.9 μS cm−1 at pH 6.5)	−43.7 in ultrapure H2O (conductivity, 4 μS cm−1 at pH 6.7)	30, 88, 101
Specific gravity	1.013–1.117	1.009–1.08	1.050–1.100	22, 32, 55, 78, 83, 120
Settling velocity (μm s−1)	0.84–1.4	0.35–1.31	Not reported	22, 78, 121

^aDepending on the species.